Signal-correcting system.



APPLICATION FILED AUG. I4. 19|B.

Patented Feb. 25, 1919 ENTTEE STATES PATENT oEEIoE.

ROBERT C. MATHES, OF NEW YORK, 1\T. Y., ASSIGNOR T0 ELECTRIC COMPANY, m'CORPORATED, 0F NEW YORK, N. Y., A CORPORATION OF NEW YORK.

SIGNAL-CORRECTING SYSTEM.

Specification of Letters Patent.

Patented Feb. 25, 1919.

receiving .Systems for use in connection with submarine cables or other high-capacity conductors.

Its object is to correct for the effect known as wandering zero and thereby to make possible the accurate reception of incoming signals.

It is well known that insignaling over high capacity cables by means of positive and negative impulses, a temporary preponderance vof impulses of one polarity will cause a cumulative charging effect in the cable, which manifests itself as an apparent shifting of the zero line in the direction 4 of the impulses,-Which, for the time being,

predominate. The distorted signal wave arriving at the' receiving end of the cable may,inother words, be saidtoconsist of two components-one, theI high frequency current reversals sent out by the transmitting station, and the other a low frequency variation, representing the fluctuating charge on the cable, followlng the momentary pre-4 ponderance of impulses of one or the other polarity. l A somewhat analogous condition may arise in the employment of signal'correcting systems such as that described in my copending application, No. 240,792, filed June 19, 1918. j

In such a system where aA transformer or an unshunted series condenser is used vbetween the cable and the receiving device the tail of the resultant arrival curve may not be sustained suiiciently to take care of a V repeated transmission of impulses of the` same polarity, and may fall ofi' to such an extent that such impulses, as for example, a number of succeedmg impulses of posltlve polarity .may be represented by actual re'-l versals of current. The point at which such a system fails will depend upon the time constant of the transformer employed, or of the circuit in which the condenser is placed.,

While it is possible to build transformers and condenser circuits with sufficiently high time constants to take care of all possible signaling"combinations, it may prove preferable to make this correction by 'employing the local correcting circuit of this invention, wherein the low frequency current representing the variation of the zero line is fed back into the system in such a way as to neutralize itself. This may be effected by the employment of a pair 'of receiving relays which are electrically biased, the one to respond to positive impulses and the other to respond to negative impulses. and to repeat corresponding signals to a local recording device or another signaling conductor. Connected to the output circuit of this relay system-is an impedance network or filter whose electrical constants are so chosen as to prevent the passage of impulses of signaling frequencies, but to permit the passage of slower fluctuations such as those 'represented by the variation in the zero line. This low frequency current is led back into the circuit of thebiasing windings of the two relays above mentioned, in such a way as to cause the fluctuating alteration yin the blasing current corresponding to the fluctuations of the zero line, but so poled as to its effect on the relays as to neutralize the effect of the iuctuating zeros upon the signals themselves.

The invention will more readily appear from a `reference to the accompanying drawing, Figure 1 of which illustrates schematically an arrangement for accomplishing the object of this invention; while Fig. 2 shows one specific form of network which is suitable for use in such a system. In the drawing, l represents a telegraphic line conductor connected to ground through the windings 2 and 3, respectively, of two polarized relays 4 and 5. Relays 4fk and 5 are provided with biasing windings 6 and .7,y supplied with current from the battery 8 to an adjustable resistance 9. The biasing of the relays is such as to maintain their armatures 10 and 11 normally against contacts which are 'connected'to one pole 12 of the' battery 13. One of. these relaysisbiased so as to respond to positive impulses, and the other is biased so as to respond to negative impulses, either relay when so responding, moving lts armature into contact with the contact stop leading t0 pole 14 of battery 13, 110

, and thus sending a local current impulse to the circuit of the responsive device 15, in one direction or the other depending upon which relay has been operated. It will, of course, be evident .that the responsive device 15 ma be any well-known type of telegraphic in icating, recording or retransmitting 1n- 1 strument, and that it may be located either at the cable terminal or at a distant point lments in the form of inductances 20 which are preferably shunted byresistances 21. By the selection ofproper values for the various capacities, inductances and resistances in the network 16, this network may be made to prevent the passage of high frequency signaling current impulses-but to permit the passage of the low frequency component representing the fluctuations of the zero line. Thus, there will be sent through the circuit including the conductors 17, 18 and the two equal resistances 22, a fluctuating l'current varying in polarity with the momentary preponderance of impulses of one or the other polarity. This will su-perimpose on the circuit through the biasing windings 6 and 7 a current of correspondingly varying direction, which current will always have the effect of increasing the bias of the o ne relay and decreasing the bias of the other. By properly poling the superimposed current with reference to the direction of the current supplied by the battery 8, this superimposed current may therefore be made to lessen the sensitiveness of the relay which responds to positive current when the low .frequency component has a positive direction, at thev same time increasing the sensitiveness of the relay whichl respondsl to negative current. Conversely, when the low frequency component is of a negative sign, the sensitiveness of the negative responding relay may be decreased, and that of the ositive responding relay increased. It wil of course be understo second type of wandering zero above referred to, a different poling of the low fre quency current with respect to the main that in the case of the v Lacasse biasing current will be required for the reason that'in this case the zero line has a tendency to move in a direction opposite to that of the -predominating impulse polarity. In either case, however, the effect of the low frequency current in the biasing circuit is opposed to the direct eect on the signals themselves. The amount of the low frequency current which is fed back into the biasing circuit may be adjusted at will by means of a variable resistance 23, bridged across the circuit of the conductors 17 and 18, as shown. It is thus seen an arrangement is provided whereby, as soon as there is a tendency .for the zero line to shift, either positively or negatively, there is produced counteracting and automatic adjustment of the sensitiveness of the two relays, so that their response may be made practically independent of the iuctuating zero, and-the signals transmitted to the responsive device' 15.will thus be practically undlstorted.'

The specific arrangement shown forl connecting the battery 8 and the conductors 17 and 18 of the low frequency circuit to the biasing circuit is not essential. Thedirectcurrent source and the low frequency source ycan in fact be'interchanged without interfering with the operativeness of the system,

the main requirement being that the direct current blaslng source and the low frequency source should be the mutually conjugate circuits.

What is claimed is:

1.-A In a telegraph receiving system, a line conductor, a pair of biased relays in circuit with said conductor and selectively responsive to signaling currents therein, and means for changing the bias of said relaysaccording to fluctuations in the apparent zero line of said signal currents. v

2. In a signaling system, a transmission line, a pair of relays in circuit with said line andv responding to positive and negative impulses respectively, a responsive device and circuit therefor, contacts insaid circuit con-a trolled by .said relays for actuating said dev1ce, auxiliary windings and circuit connections forbiasing said relays in opposite directions, a branch circuit extending from the circuit of said responsive device to said biasing circuit, and means in said branch circuit for preventing the passage therethrough of impulses of signaling frequencies while permitting the passage of relatively low frequency current variations.`

In witness whereof, I hereunto subscribe my name this 5th day of August A. D., 1918. l 

